The present invention relates to an analytical furnace and particularly to an analytical furnace having a predictive temperature control.
Many laboratory analyzers employ combustion or other types of furnaces which heat and/or combust a sample for the determination of chemical elements in the sample. One type of analyzer is a thermogravametric analyzer which employs a furnace, the temperature of which must be carefully controlled. The thermogravametric analyses of materials provide important information as to moisture content, volatiles, ash, or fixed carbon, as well as weight loss or gain on ignition. Materials, such as coal, coke, graphite, flour, dough, plant tissue, feeds, fertilizer, food stuffs, chemicals, rubbers, plastics, ceramics, minerals, soils, sediments, and paper, are all capable of thermogravametric analysis utilizing ASTM standards, which detail the requirements for determining the moisture, volatiles, fixed carbon, ash content, and ignition content of materials. The determinations are made by first weighing a sample to be analyzed and then subjecting the sample to a well controlled time/temperature profile in a controlled atmosphere and weighing the sample during the control period to determine weight loss at different temperatures. Well known mathematical formulas are then employed to calculate the moisture, volatiles, fixed carbon, ash, and ignition content of the material. It is of primary importance that the temperature profile is accurately known and precisely controlled, particularly where sample material can loose discrete percentages of its weight at distinct temperatures.
Prior art analyzers performing sample analyses and analyzers performing multiple sample thermogravametric analyses typically use a furnace having a single temperature sensor, which, although providing adequate analysis information, can suffer from slow operation and less than desirable accuracy in performance. Thus, there is a need for an analytical furnace, such as for use with a thermogravametric analyzer in which the temperature within a sample-holding crucible is accurately determined and can be precisely controlled. There further exists a need for an analytical furnace which improves the speed of analyses and which has repeatability from analysis to analysis and reproducibility from instrument to instrument so that accurate, fast analyses can be obtained.